Electrical contact device



April 5, 1960 E. .J. HENLEY ELECTRICAL CONTACT DEVICE 2 Sheets-Sheet 1Filed Feb. 20, 1958 INVENTOR Edwand llle/nle ATTORNEY April 960 E. J.HENLEY 2,931,877

ELECTRICAL CONTACT DEVICE Filed Feb. 20, 1958 2 Sheets-Sheet 2 SIGN ALSOURCE Z 3a 37 TO INPUT x'f fcs OF AMPUF'IER o 38 "57 '5 y III l ,.6

SIGNAL- souaca INVENTOR ATTORNEY SW68 P m 2,931,877 ELECTRICAL CONTACTDEVICE Edward J. Henley, Fanwood, NJ.

Application February 20, 1958, Serial No. 716,356

3 Claims. (Cl. 200166) My invention relates to electronicorgans,,particularly of the type wherein individual tone sources areconnectted to; amplifier and reproducing means by key actuated:switches, and has for its primary objectto provide an improvedelectrical contact for said switches. I}

1 -It is another object-of my invetnion to provide an elecitricalcontact which generates transient and random I 2,931,877 P t .Apr- 19(59elastically deformable, electrically semi-conductive material interposedbetween a stationary contact element or bus bar 12 and a movable contactelement or finger 13. The filament 11 and the movable contact element 13have arcuate surfaces, preferably cylindrical, and are shown disposed atright angles with respect to each other to afford a point contact, as attheir points of tangency. Since the filament 11 is elasticallydeformable, the point contact rapidly changes to a contact withsubstantially ;noise voltages upon initial'closure thereof, suchtransient voltages diminishing as the closure pressure increases.

It=is still another object of my invention to provide an electricalcontact having a highimpedance compared :to the. tone source impedanceat the moment of initial closure and having a lowimpedance compared tothe tone :source at full closure.

It isyet. another object ofmy invention to provide an electrical contacthaving a large change in resistance with :relatively small motion ofeither contact element.

' It isia further object of my invention to .provide an i (electricalcontact which is adaptable to economical con- :struction of a contactsystem wherein a pluralityof tone sources ,is connected throughelectrical contactsof my -2illVCfltiOIlIO common bus bars.

It is still a further object of my invention ,to provide :an electricalcontact which is durable in construction, economical in manufactureandreliable in service.

Other and further objects will be obvious upon an understanding of theillustrative embodiment about to be described, or will be indicated inthe appended claims, "and various advantages not referred to herein willoccur to-one skilled in the art upon employment of the invention inpractice.

A preferred embodiment, of the invention has been Fig. 4 is a sectionalview taken along line 44 of w Fig. 2 in the direction of the arrows;

Fig. 5 is an enlarged, perspective view showing a contact finger inoperative contact engagement with its associated bus bar illustratingthe enlarged surface contact area following the initial contact;

Fig. 6 is a schematic view of a circuit including the elements shown inFig. l; i

Fig. 7. is a typical signal of a tone generator or signa source;

Fig. 8 is a curve illustrating introduction of transient noise voltagesas initial contact of the finger upon the bus bar is established;

Fig. 9 is a sectional view showing a contact assembly with a pluralityof associated contact fingers and bus bars;

block 18, as shown in Fig.1.

greater area, .as the finger 13 is depressed against the filament '11.Because of the high resistance and'uncer tainty of the initial contact,transient electrical fluct'ua tions are introduced into the appliedsignal. andthese fluctuations produce a sound similar to the initialhiss'of air that occurs when 'a' valve is opened under a pipe inapipeorgan. I f

I find that the initial hiss characteristic lends character to the toneand simulates musical instruments better than the conventionalelectrically noiseless, progressive contact means, such as that shown,for example, in Mork Patent 2,575,230. Also, my contact arrangement pro-.vides means for closing an electric circuit in a manner which isneither instantaneous nor sluggish, as insaid Mork patented arrangement.

Referring again to Figs. 1 to 4, the contactassembly 10 comprises a basel ton which are shown a mounting block 16 for a playing key 17 andamounting block 18 for a pile-up'ofthe fingers, filaments, etc., as willappear hereinafter. A resilient element or fiat spring 19 interconnectsthe mounting block 16 and the playing ke'y I'Z.

Upon the upper surface of the mounting block I8is showndisposed apile-up of three insulating strips,v a lower strip 21 and an upper strip22 that overhang the Each of these strips has a slot 23 (Figs. 2 and ,4)inthe overhanging" portion for registration and guidance of an actuatingelement 2.4.

The third strip 26 is'shorter in depth than theother two strips and hasits front edge flush with the face of the block 18. An opening 27 isformed in the central, front portion of the strip 26 to provide forvertical movement expanded portions" of theifilament, upon,cprnpression' thereof during assemblyin order to' maintain the filamentin contact with the bus 12. To the upper surface of'the lower strip 21is afiixed the stationary contact or bus bar 12, in a recess, so thatits upper surface is flush with that of the strip 21; or the bus 12 maybe preferably etched onto the strip 21 by conventional means. The threeinsulating strips and block 18 are fastened'together to the base 14 byscrews 30 in the usual manner.

Asseen particularly in Figs. 3 and 4, the finger 13 passes through anopening 32 in the actuating element 24, whereby downward movementthereof, produced by the key 17, will lower and causethe finger to press3 Y vid'ed -with a set screw 33 having a head 34 at its lower endforengagement with the actuating element 24. A slot 36 at the upper end ofthe screw 33 for engagement by a screw driver enables the contact traveland pressure of the finger to be adjusted as required. i

7 To the left end of the contact. finger '13, as viewed in Fig. l, isconnected one terminal or a resistor 37, the other terminal of theresistor being connected to a signal source 38 and thence (Fig. 6) toone side of the input of an amplifier (not shown). This resistor 37represents the impedance of an associated electric circuit or can beused to build out the impedance of the associated circuit to the desiredvalue. However, it is within the contemplation of my invention to employa filament or elastomer 11 having sufiicient resistance to effectivelydetermine the total circuit impedance. Itwill be noted in Fig. 6 thatthe bus 12 is connected to the other side of the input of the amplifier.

In operation, upon depression of the playing key 17 the actuatingelement 24 is lowered by the head 34 of the set screw 33 to in turndepress the finger 13 into initial, point contactwith the elastomer 11.Prior to this contact and, while the finger 13 and elastomer 11 areseparated from each other, the tone from source 38 may be represented bya sinusoidal curve 39 shown in Fig. 7; Upon said point contact thetransient noise voltage produces at the bus 12 the modified tone fromthe source 38 represented by the curve 41, shown in Fig. 8, wherein itwill be noted that the amplitudes of the sinusoidal curve 39 have beensubstantially reduced by the high, initial resistance value of the pointcontact. As the depression of the key 17 continues, see Fig. 5, theresistance of the larger area contact between the finger 13 and theelastomer 11 drops to produce the desired, final tone.

As a modification, the elastomer 11 and bus 12 may be combined into theform of a cable, as seen in Fig. 11. Here, a bus 12' is shown as acentral conductor surrounded by an elastomer 11. The operation of thismodification is similar to that heretofore described, from the initialcontact to the depressed contact of finger 13.

At this point it may be mentioned that the elastomer 11 may beconstituted by any of a number of commercially available natural orsynthetic rubber compounds having an electrical resistance in the orderof 100 to 200 ohm-centimeters. The contact finger 13 is preferably .012to .015 inch in diameter of Phosphor bronze wire plated with a corrosionresisting metal, such as gold.

The metallic bus 12 or central conductor 12 may be of tinned copperwhile the three insulating strips 21, 22, 26 and actuating element 24may be of phenol fiber.

For most satisfactory operation the impedance of the source 38 is about100,000 ohms. At the moment of initial contact by the finger 13 upon thefilament or elastomer 11, the contact resistance is about one megohm ormore." As the actuating element 24 is depressed further, the elastomeris deformed by the finger 13 to increase the'contact areatherebetween'and thus decrease this resistance to a few thousand ohms.

From the foregoing description it will be seen that my inventionprovides an improved electrical contact for switches particularlyadaptable for use in electronic organs. While only a single contactarrangement of finger 13 and elastomer 11 has been described in theforegoing, it is, of course, required that a plurality of such contactarrangements be operable by a single actuating element 24 in order toobtain the desired tones. Such a multiple arrangement is shown in Figs.9 and 10, wherein the actuating element 24' is adapted forsimultaneously moving a plurality of fingers 13 into contact withassociated elastomers 11, arranged in superposed relation ship.

As various changes may be made in the form, construction, andarrangement of the parts herein, without departing from the spirit andscope of the invention and without sacrificing any of its advantages, itis to be understood that all matters are to be interpreted asillustrative and not in any limiting sense.

What is claimed is:

1. An electrical contact device comprising a stationary, elongatedmetallic contact element, amovable, elongated metallic contact elementhaving an arcuate surface, and an elongated, elastically deformable,electrically semiconductive member having an arcuate surface interposedbetween said contact elements in linear relationship to 'said stationarycontact element, said movable contact element and said semi-conductivemember being disposed at right angles with respect to each other andsaid movable contact element being adapted to engage said semiconductivemember to establish a circuit connection between said movable contactelement and said stationary contact element.

2. An electrical contact device in accordance with claim 1, wherein saidmovable contact and said semi-conductive member are each circular incross section. I

3. An electrical contact device in accordance with claim 1, wherein saidstationary, metallic contact element and said semi-conductive member areformed as a cable with the stationary, metallic contact elementconstituting a core thereof and the semi-conductive member as thesurrounding material around the core.

References Cited in the file of this patent UNITED STATES PATENTS 7Germany July 3, 1936

